The purpose of Core A is to provide assistance with state-of-the-art measurements of reactive oxygen species (ROS) and nitric oxide (NO) in vascular cells and tissues for the participants of the PPG. CORE A will assist with preparation and processing of various biological samples for analysis using Electron Spin Resonance (ESR) spectroscopy. ESR spectroscopy with a spin trapping technique is one of the most direct and unequivocal methods for high sensitivity quantitative detection of reactive oxygen species even in strongly scattering media using minimal amounts of biological material. This Core facility has existed since 1999 and has supported studies of superoxide radical and nitric oxide in vascular cells in several publications from Drs. Griendling and Harrison. This facility will significantly enhance the work of the individual labs and will clearly improve collaborations between participants of the PPG project. Specifically, the Electron Spin Resonance Core will: 1. Offer expertise, facilities, and training for individuals in performing measurements of ROS and NO using ESR spectroscopy. 2. Provide assistance with state-of-the-art in vitro and ex vivo measurements of ROS and nitric oxide in vascular cells and tissues for participants of the PPG. 3. Develop techniques and refine existing methods for measurement of ROS and NO in vascular tissues.